(1) Field of the Invention
The present invention relates generally to acoustical processors and more particularly to a method of acoustic processing for acoustic image classification.
(2) Description of the Prior Art
Underwater systems capable of performing the function of target classification typically rely on acoustically derived measurements of the physical extent of the targets or false targets as part of the classification process. The measurements, gathered from spatially separated sensors generating split beams, are processed to form an acoustic image of the object in question. Characteristic parameters of the object (length, width, etc.) are then extracted from this acoustic image and used to determine the classification of the object.
Split beam processing is one conventional approach to the image formation process. Offset phase center beams (left/right, up/down) are used to generate angle estimates of threshold crossings produced from a sum beam output. The underlying assumption behind the split beam processor is that only one scatterer exists in each range bin of the acoustic image. Detecting the return from that scatter, the processor estimates the off-boresight angle to that scatterer. The estimated scatterer locations are then processed further to generate the image. The assumption of a single scatterer per range bin places a limitation on the usefulness of this approach. Many objects of interest in the classification problem can have significant cross range extent. The single scatterer model does not hold for these objects and the resulting image ma be difficult to classify.